We are following the synthesis of the parvovirus, KRV, as a tool to understand both cellular and viral mRNA synthesis. Viral specific RNAs are synthesized in the nucleus, processed, modified and transported to the cytoplasm, presumably by the same mechanism as cellular mRNA biosynthesis. However, viral RNA synthesis involves fewer species of synthesized RNA than total cellular RNA. Hence, it is a simpler system for study than the complex eukaryotic cellular RNA. The viral RNAs can be identified as viral specific by hybridization, gel electrophoresis, restriction enzyme analysis and by Northern and Southern blotting techniques. We have developed a cell free system in isolated nuclei which can synthesize viral specific RNA. We have also isolated the viral RNAs from infected cells and used the viral RNA to synthesize in vitro viral proteins. Further study should yield more detailed information on the requirements and conditions needed for RNA and protein synthesis in the infected and normal eukaryotic cell.